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TILTED GLAZING:
ANGLE-DEPENDENCE OF DIRECT SOLAR HEAT GAIN
AND FORM-REFINING OF COMPLEX FACADES
by
Won Hee Ko
A Thesis Presented to the
FACULTY OF THE USC SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE
May 2012
Copyright 2012 Won Hee Ko

Contemporary cities are in a transition phase from primarily planar surfaces to a more dynamic urban fabric. One of the main contributors to this change is the development of shaped high-rise buildings that are in strong contrast to box-shapes of the past. This tendency makes accurate building energy simulation more difficult. Although sophisticated software exists to predict the performance of buildings and help architects and engineers make better decisions that reduce energy use, such programs are generally not able to deal with complexities of unconventional façade design. This is especially critical in regard to fenestration of high-rise office buildings, which have a large proportion of glazed area. Therefore, it has become important to improve the ability of energy software to deal with more complex façade designs. ❧ This research thesis focused on the effect of angular dependence on direct solar heat gain (DSHG) from tilted glazing. Variables that affect the optical properties of inclined glazing have been researched. One of the main variables, angle of incidence was chosen to be investigated in this research. The prescriptive path in ASHRAE 90.1 (ASHRAE STANDARD: Energy Standard for Buildings Except Low-Rise Residential Buildings) defines requirements of glazing properties depending on climate and building type regardless of the angular dependence of DSHG. For example, current SHGC is independent of angle of incidence. This can lead to errors in the building performance prediction. To improve DSHG calculation, a master spreadsheet that includes incident angle calculation based on the specific location, time and surface azimuth was developed. The effect of incident angle was reflected in DSHG calculation based on perpendicular direct incident solar radiation and the effective SHGC to produce the spreadsheet. Using this spreadsheet, one can predict the amount of DSHG through each area of tilted glazing, with time-dependence throughout the year. ❧ Next, an algorithm was developed in Grasshopper (a plug-in for Rhino 3D), linking to the master spreadsheet. This algorithm can extract the surface azimuth and tilt angle of any surface from a given faceted form of building in Rhino, and the surface information is input back into the spreadsheet to calculate the DSHG of the surface. Based on this process, one can easily see the total DSHG of a whole building. By using the algorithm, the DSHG values of a simple box-shaped building and a building with tilted geometry were obtained. The difference between the DSHG values clearly shows the importance of accounting for the angular dependence of glazing, which is not generally included in building simulation programs, energy codes, and even architects’ perceptions. Without visual editing software such as Grasshopper, this process would have been possible only with time-consuming calculations and multiple iterations in the past. At the present time, technical innovation allows such studies to be conducted in an easy, quick and accurate way. This algorithm was developed further in Grasshopper to demonstrate form refinement of faceted building facades with an emphasis on the angle-dependent DSHG of glazing, a key factor for determining cooling and heating load. The intent is to provide a visual tool where architects could fine tune their initial ideas for the massing of a building and help them determine a better angle of glazing for the building and its overall geometry in a specific climate zone.

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TILTED GLAZING:
ANGLE-DEPENDENCE OF DIRECT SOLAR HEAT GAIN
AND FORM-REFINING OF COMPLEX FACADES
by
Won Hee Ko
A Thesis Presented to the
FACULTY OF THE USC SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF BUILDING SCIENCE
May 2012
Copyright 2012 Won Hee Ko